Glow-discharge apparatus and method of operating the same



May 3-, 1927. P- THOMAS v GLOW DISCHARGE APPARATUS AND METHOD OF OPERATING THE SAME Filed Nov. 1 1922 INVENTOR P/vimps Thomas 7 BY /7- I W WITNESSES:

mrsp srArs-s PATENT, OFFICE. a

@ PHILLIPS THOMAS, or EDGEWOOD, PENNSYLVANIA, assrcuvon To wEsTmenoUsE ELECTRIC & MANUFACTURING COMPANY, aconron Tron-or PENNSYLVANIA.

GLOW-DISCHARGE nrrnn'jmu's AND METHOD or orEimTme THE smu- Applicatiqn filed N ove mber 14,1922. Serial No. 600,824.

My invention relates to telephonesystems and apparatus and more especially to sound- Wave translating devises. v 1

In its broad aspect, an ,important' object 5 of my invention is to provide a tfanslating' device adapted to effect an interchange of energy between a flu1d medium subject 'to vibratory motion and an electrical circuit a carrying vibratory electrical currents.

tion is to provide translating means wherein sound waves are faithfully translatedi'nto correspondingly modulated electrical energy without impairing the quality, tone and quantity of the translated energy.

Another object of my'u'nventwn is to provide an-improved translating deviceof the glow-discharge type, wherein the intensity of the response to pressure variationsis independent of the frequency of such variations Still another object of my invention is to provide a glow-discharge apparatus embodying such design as to eliminate the so-called ground? tone heretofore present in the operation of most discharge apparatus. A further object of my invention is to provide means for properly shielding the incoming and outgoing circuits associated with the glow-discharge apparatus, whereby the same may be protected from adjacent, transmitting systems.

A still further object of my invention is the glow-discharge from the undesirable effects of disturbing drafts and currents of air but also tends to accentuate the effects of the higher frequency pressure variations on .the glow discharge, all as will appear more fully hereinafter. H 5 1 With' these and other objects and applications in view, my invention further con-- sists in the nature, the mode of operation, the constructional details and the circuit arrangements hereafter described and claimed and illustrated in the accompanying draw-v 1 ing, wherein Figure 1 is a diagrammatic view 'of circuits tion,

Fig. 2 is a greatly enlarged detail view of the main dischargeelectrodes of Fig. 1,

and apparatus embodying my inven together with a third and fourth electrode and means for shielding the positive column,

More specifically, an object of my invenduring experimental work, the ener to provide ameans which not only protects Figzlfi is ai greatly enlarged detail 'view ofth ef'negat-ive: electrode of Figs.- '-1 and-2, lllustgatin'g the form of the discharge surface of the tip when made of material hay inga high melting point, j i a so] ,1Fig."4 isa similar view bufshowing the nature of the tip discharge surface Wh8Il' 'made of' material having a. low melting pointg Fig. 5 is a detail view showing alternative means for protecting the discharge from undesirablealr-currents,- and "\Fig. B is adetail view illustrati an ar rangelnent for intensifying the effect .of the higher-frequency pressure variations; H

In-the embodiment of my invention shown in the drawing, a pair of'elect'rodes 1, and 2, having'spaced sparking tips '3 -and 4,;respectively, ar'e connected by conductors 5 and 6 to the positive vand negative terminals; respectively, of a source of direct current energy (not shown). The negative supply conductor 6 is connected to ground by means of a ground conductor 7. i

A resistor 8 is connected-in series-circuit relation 'tO OlIB'Of the supply conductors, say and serves to maintain the currents through the discharge substantially constant during variations in the voltage-current'characteristic of the discharge caused by pressure changes, all as hereinafter do; scribed. In the particularsystememployed source h d n electro-motive force on t e order-- 0 6 00 volts and the resistance of the resistor 8 was-on the order of a megohm. When the tips 3 and 4 of the discharge electrodes are separated, say for a systern havin the constants just mentioned, a

discharge is established between the said at) tips which diii'ers from the ordinary discharge of the arc type in the following important respects: the tips are relatlvely cool; there is substantially no vaporization,

melting or burning of the same, in compari- 1 00 son with that present in discharges of the arc type, the customary hot spot, character istic of the ordinary arc, is absent, and the discharge, when formed between electrodes I of certain materials, as s'pecified hereinafter, 10

takes place in a relatively steady, smooth and unfluctuating manner. The latter operating characteristic of the glow discharge is of especial importance, inasmuch as fluctuations in the-operations f the discharge no.

' between the tips 3 and may be such as to cause potential or current variations which .are comparable in magnitude to the variations caused by sound waves, as will be apparent in the light of the following description. The glow discharge, which is established 4, comprises the following portions arranged in their respective order between the negative tip 4' and the positive tip 3, viz, a cathode glow 9, which is in immediate contact with the negative ""tip 4, a cathode dark space 11, also knownand when thecurren as Crookes dark space, a negative light-12, which is perceptible to the eye, a Faraday darkspace 13* and a positive column 14 which terminates on the tip 3 of the positive electrode 1 and which may be perceptible to the eye, all as illustrated in a greatly anagnified detail view in Fig. 2.

When the dischar e is once established therethrough is maintainedv substantially constant, the potential 7 drop thereacross varies with pressure and ble frequen cy range.

also with the frequency of the pressure variations in the higher portions of the audi- The result of such frequency variations onthe sensitivity of the. discharge is to cause distortion of the higher notes in the audible-frequency range. After considerable experimental work,

it was found that the sensitivity of the portion of the discharge including the positive column 14 varies with the frequency of the' impressed pressure varitions, whereas, the sen sitivit of the Faraday dark space 13 was found to be substantially independent "of such frequency changes.

-Accordingly, apparatus was arranged I which made possible the detection of presbordering on the sure variations in the Faraday dark space 13. The apparatus comprises a thirdelectrode 15, which is disposed .in the discharge at the'free end of the positive column 14, a fourthelectrode 16. which'is disposed in the portion of the Faraday dark space 13,

cathode glow 12, anda repeater device 17. The third and fourth electrodes '15 and 16 are provided with perforations 18 and 19, respectively, on the order copper "f1- fourthelectrodes 15. and-16-, in the presence v v may be translated j-ilpto amplified currents of similar wave form IIJI y "i fil of .014" in appear hereinafter. Advance diameter and are positioned with the perforations in the path of the discharge, Improved results were obtained by employing third and fourth electrodes made of Advance material for reasons which will material beapproximately ing an alloy consisting of sixty per cent.

forty per cent "nickel and ,The alternating component of voltage .iwhich is established between the third and pressure ,..variations,

Expressing thel a'same upon the grid and elements 21 'and 22,. respectively,

' nected to inasmucli as contact of the repeater device 17, which includes,

in addition, aplate element 23. The third electrode 15, which is disposed immediately adjacent to the positive column 14, is conthe grid 21 by means of a conin series-circuit relation doctor 24 including,

25. The

therewith, a grid-biasing condenser condenser 25 has a negligible impedance to currents of sound-wave frequency and may also serve to prevent the so-called quiet voltage drop between the third and fourth electrodes 15 and 16,from operating to block the tube 17:

The fourth electrode 16 is connected to the filament 22 of the repeater device 17 by means of a conductor 26. The conductor 26 may be connected to ground by means of a ground conductor 27. A condenser 28, having a low reactance'to currents of audible frequency, is included in the conductor 26 between the fourth electrode 16 and the vent the conductor 26 and the ground connection 27 from operating to short-circuit a portion of the direct current traversing the discharge. A grid-leak resistor 29 may be ground wire connection 27 and serves to preincluded in shunt relation to the grid and 4 filament elements 21 and 22, respectively, in

order to control the intensity of the negative charges which are accumulated on the grid 21. y a

A plate-filament circuit for the tube 17 in.- cludes a SOllI'CBz-iil of direct-current energy and a high impedance resistance coupling device 32. The potential variations which are establishedacross the resistor device 32 -when the glow discharge is subjected to having 'a diameter small in comparison to.

that of the positive column 14. As shown in Fig. 2, the free end of the positive column 14 extendsthrough the perforation 18.without engaging the. walls thereof, forming a small tip portion 35. ,After long operation, the third electrode 15 becomes slightly heated but does not assume the temperature of the glow discharge. The fourth electrode 16, as previously stated, is positioned just out of contact with the negative light 12, therewith will-cause its an amplifying device (not destruction, the temperature of the negative light 12 being far above the melting point of the fourth electrode 16. i

In the development ofmy invention, considerabledifliculty was experienced in estab lishing and maintaining a glow discharge between the discharge electrodes. The dis charge, when once established, was likely to be very noisy in operation. It was found impossible to-establish a glow discharge between electrodes of manganese, iron, nickel,

carbon, aluminum and molybdenum, While the discharge which was'established between electroded of tungsten, silver and platinum was exceedingly noisy. Greatly imprgved :results were' obtained by employing electrodes of copper, but-such electrodes did noteffect the elimination of a slight ground tone which still persisted during the operation of the discharge. Furthermore, the dis-- charge was subject to intermittenteabrupt changes in gradient which completely overshadowedthe relatively slight changes effected by the pressure variations of sound waves.

The undesirable operating characteristicsjust mentioned. are believed to be partly caused by thehigh melting point of the "negative tip 4 in. the instances just; mentioned When the light discharge has been 37. to the cathode glow 12.x When such acin Fig, y

1 The ioniz'ationestablished in the case of" tion occurs, the operation of the discharge is naturally disrupted.

This undersirable operating. characteristic is overcome by the provision of a cathode tip of relatively low meltingmaterial, as, for instance, Advance wire.

stated, this substance is' an alloy of copper and nickel-in the general-proportions of'--6O to 40. When the glow discharge is established between such electrodes, the eifect of xthe discharge is to cause the negative, tip" 4 to burn away to a convex point thereby iorming a convex surface 38, as illustrated the electrode having the low melting point is distributed with substantial uniformity throughout the entire cathode dark space. 11 by reasonof-the form of the surface'of,

the negative tip 4, thereby avoiding any tendency for'a short-circuit between the end.

of the negative sparking tip 4 and the oathode glow 12 and the resulting interruption in the operation ofthe discharge. 9 The so-called ground tone is further. re-

. duced and the general efiiciency of operation As previously of: the discharge is increased by making the" negative tip 4 of a material having a low heat conductivityfthat is, a material which permits the currentstraversing the, glow' discharge to heat lncrelytl'leend of the ne ative sparking tip 4 to such temperature tiat it becomes a source of ionization.- \Vhen thetip 4 becomes a source ofionization, as just desc'gi bed, the Faradaydark space 13 length-.

ens, resulting in more stable operation of the discharge. L Theparticula'r need for arelatively'long Faraday dark space 13 was observed when the tip of the positive column 14'Would extend across the Faraday dark space 13. to the negative l i ht 12 in the presence of. excessive modu ationftherebydisrupting the discharge.

'tiye tip 4' are so adjusted that, when the proper temperature conditions obtain at the The diameter and the length of the negaend of the negative tip 4. as just described,

the diameter of the negative light '12 is approximately the same as that of the cathode 'tip "4. A greater amount 01? current than the value necessary to effect. such relation causes loud, high-pitched whistling noises in the operation of'the 'discharg'e, whereas a lower currentcauses sibilant hisses. Alatitude of approximately ten ercent, plus orminus, was found to be permissible, for a circuit having the constants previously men tioned. ,The dimensions of the negative sparking tip 4 employed inexperimental .work' were .075" in diameter and 9 in length. The angle'of the. face 39 of the electrode 2, with respe ct to the longitudinal axis thereof, was alsd found to afl'ect; the operation of the discharge. Optimum operation'of the discharge was obtained with an angle of approximately 30.

' en operating my invention in t cuitof alarge transmitting station, was found necessary to provide shielding means for the several conductors associated with the glow-discharge apparatus. This was ciraccomplished by. providing the incoming -conductor5 with a"shieldj41 grounded by aground conductor 42 and by providing the outgoing conductors 24 and 26. leadingfrom thethird and fourth electrodes 15, and 16,

respectively, withlshields 43and 44 grounded by conductors '45 and 46, respectively,

eration of theglow discharge was exceedingly unsteady since the 'conductors and shields functioned as condensers to periodi- It was then found, however, that, theop cally extinguish the norm'alglow ,discharge. I

The path traversed by one such discharge comprises the condensemformed between the lead 5 and'the'shield 411% the groun' conductor 42. a portion 47 of theconductor-G" between the ground conductor 7 and the neg-Y ative electrode 2, the negative electrode 2,

' the glow discharge andthe positive electrode 1. This undesirable condition was overcome 1/ per carbonate are broken away posedto the disturbing'eifects by inserting a resistor 48 in the positive ductor 24 and the shield 43 extends from the shield 43 throughthe ground connection 45,

the ground connection 7, the portion 47 of V the negative supply conductor 6, the negative electrode 2 and the space between the negative electrode 2 and the third electrode 15 and the third electrode 15 to the conductor 24. In the case of the fourth electrode conductor 26, a somewhat similar circuit is formed which extends from the shield 44 through the ground connection 46, the

5 ground connection 7', the portion 47 of the conductor 6, the negative electrode 2, the space between the negative electrode 2 and the fourth electrode 16 and the fourth electrode 16 to the outgoing conductor 26.

The condenser effect of the shields 43 and 44 is overcome. by inserting a resistor 49 ,in the portion 47 between the ground connection 7 and the negative electrode 2. The resistance'of both stabilizing resistors 48 and 49 may be on the orderof 100,000 ohms or thereabouts. c

Further improved results may be obtained by minimizingthe effect of the positive column 14 upon the characteristic variations of the glow discharge in the presence of pressure variations, as caused by sound waves or drafts of air. In Figs. 1 and 5 is shown/one particular means for producing the above mentioned effect comprising a tubular member 51 of insulating material whichds supported from one end by the positive electrode 1 and which carries the third electrode 15 from the other end there'- The use of copper for the third electrode 15 has the disadvantage that, during the periods when the discharge is not in operation, copper carbonate is formed around the perforation 18 contained therein. When the I discharge is established, the particles of copfrom the i third. lectrode 15 and drop into the positive column inclosure formed byxthe tubular member 51, causing the discharge tobecome noisy in operation.

such shi lding means,

A as just described, while affording protection "for the positivecolumn portion 14'of the glow discharge, "leaves the remaining. portions thereof exof' drafts of air. Furthermore, finely divided particles of dust in the air, as iron sulphide, were found to interfere with the normal operation of the discharge. Accordingly, an inclosing member 52 was constructed, as shown in Fig. 1.

The structure comprises a 'casing 53 of cylindrical shape having open ends 54 and 55. .Thedischarge electrodes'l and '2 are carried. by said casing 53, with the and apparatus directly sparking tips 3 and 4 associated therewith disposed therein. .The open ends 54 and 55 of the casing are closed by reticulate members 56 and 57 respectively, as, for instance, pongee silk or felt.

When employing such structure in a closed room, it-was found advisable to cause the sound waves to enter the chamber formed by thecasing 53 from one side thereof only, thereby tending to minimize the distortion caused by the sound waves reflected from the walls of the room. The end of the casing, say 54, facing the origin of the sound waves may be covered by pongee silk 56,

whereas the remaining end 55 may be co.V

ered with heavy felt57. The heavy felt 57 also serves to prevent the reflection of the sound waves within the casing 53 itself.

The electrodes 1 and 2 are preferably vertically positioned within the casing 53, with the negative electrode 2 uppermost. Such arrangement'was found to render the operation of the discharge more steady. The reason for this is thought to be due to the fact that, when the negative electrode 2 is vdisposed directly beneathrthe positive electrode 1, travel of the electrons emanating from the negative added by the upper rents'caused by the heating of the air in the lower portions of the chamber formed by the casing 53. -As can be seen, notobtain with the negative electrode 2 uppermost. i In Fig: 5 is shown an alternative structure for protecting the glow discharge from the effects of air currents and comprises a shielding tubular member 58 covering the tip 4 to the positive tip 3 is greatly movement of the air 6ursuch' effect does cathode dark space 11 and the'negative light 12 and carrying the fourth electrode 16, the

result being substantially like that effected by the tubular structure the positive electrode 1. It will be notedthat the structure shown in Fig. 5 *protection' for the Faraday dark space 13 but this space, however is substantially unaf fected by drafts of air tending to extinguish the discharge.

In Fig. 6 is shown a holder 52of the doublehorn type for discharge electrodes 1 and 2, the same being designed to amplify the effects of the pressure. variations in the provides no 51 associatedwith higher portions of the audible-frequency range to a greater extent than in the lower The arrangement comprises a cyportions. I

casing 61 forming oppositely exlindrical tending horn-like chambers 62 and 63, the larger ends 64 and 65 thereof being exposed and the smaller ends 66 and 67 thereof being interconnected respectively, to form a common portion 68. The'electrodes 1 and 2,

which are carried b .the casing 61, have their discharge tips isposed in spaced relation in said portion 68. By making the resonant frequency of the horn-like chambers 62 and 63 well up in the audible-frequency range, the effects of the higher-frequencypressure variations are accentuated. In operation, it was observed that the horn would partially convert simple pressure changes at the glow discharge to actual vibrational air currents, thereby increasing the original ef-' I be a glow discharge and will continue to be a glow discharge and not change into an are, I find that the source of potential must be high and that a current limiting device must be used. In addition to the specificdimensions already stated herein, the following actual constructions are noted. In one specific embodiment of my invention, I employed a source of somewhat more than 4000 volts with a resistance in series between it and the discharge device of approximately one megohm. In another specific embodiment of this invention, I employed a source of 4200 volts, together with a current limiting device which restricted the current to one milliampere. The current limiting device used ,inthis instance was a saturation tube.

A characteristic difierence between the glow discharge and the arc is found in the relation of current to voltage. In the arc the current is much greater and the voltage much smaller than in the glow discharge. Another characteristic difference is that with the glow discharge the electrodes are relatively cool, never becoming incandescent, whilewith an arc the electrodes are hot and the cathode is usually more incandescent than any portion of the arc'itself.

An application of structure just described is in the translation of sound waves pro duced by a telephone receiver back into modulated currentsthrough the medium of the glow-discharge apparatus, since the effect of the telephone system on modulated currents, especially when transmitted over long distances, is to decrease the intensity of the higher-frequency currents, while the effect of the double-horn arrangement is to accentuate such frequencies.

While I have described my invention as embodying a circuit arrangement having certain specific values, and while I have shown certain embodiments of my invention, it is apparent that various changes and modificaf tions may be made therein without depart lngfrom the spirit of my invention. 'I de sire, therefore, that only such limitations shall be imposed. thereon as are indicated by the appended claims or demanded by the prior 'art.

1 claim as my invention:

1. In combination, a pair of spaced electrodes, means for establishing a glow discharge therebetween, said discharge including a Faraday dark space and other portions, and means responsive to variations of an electrical characteristic of said dark space only for delivering corresponding electric currents. j

2. The method of effecting a transfer of energy between a fluid medium andan electrical circuit which consists in establishing a glow discharge in said circuit having a 85 Faraday dark space and other portions, subjecting said medium to varying pressures and detecting variations in an electrical chzliract'eristic of said Faraday dark space on y. y

3. sound-wave translating device comprising a glow-discharge apparatus in a medium responsive to pressure variations due to sound waves, means responsive only to changes in a characteristic of theFaraday dark space resulting from pressure variations in said medium for delivering corresponding electric currents and means for minimizing the effect of the positive column upon the characteristic of the dischargedn the presence of sound-wave disturbances.

4. A. translating system comprising a pair of spaced discharge electrodes, means for establishing therebetween a glow discharge, said discharge comprising a Faraday dark space, a pair of spaced electrodes positioned in said Faraday dark-space, said last-mentioned pair of electrodes having perforations disposed substantially in alignment with each other and with said electrodes and a repeater device for detecting Variation in the voltage-current characteristic of the portion of said discharge between said last-mentioned pair of electrodes.

5. A translating system comprising a pair H5 of spaced discharge electrodes,.-means for establishing therebetween a glow discharge, said discharge comprising a Faraday dark space, a second pair of spaced electrodes positioned in said Faraday dark space, and a repeater device having input conductors connected respectively to said last-mentioned pair of electrodes, one of said conductors being grounded and including a capacitance between the ground connection and its 'coand negative terminals of a glow discharge device, means for grounding the negative terminal, a pair of spaced electrodes interposed between said discharge elements, a repeater device having input elements, conductors operatively associating said input elements to said spaced electrodes respectively, means for groundingone of said conductors and a capacitance reactance included in said grounded conductor between the ground connection and its co-operating elec trode. i

7. In an electrical system, a pair of spaced electrodes constituting the positive and negative terminals of a discharge device, supply conductors for said electrodes, means for grounding'the negative supply conductor, a third electrode positioned intermediate said pair of electrodes, an outgoing conductor for said third electrode, means for shielding predetermined portions of the several conductors and means included in said negative supply conductor between the ground connection and the negative electrode for preventing the capacity eliects between the'conductors and renderthe discharge unsteady.

8. A translating device comprising a pair of spaced electrodes constituting the positive and negative terminals of a glow-discharge apparatus, the negative terminal being substantially vertically positioned above the positive terminal. 1

9. In combination, acasing comprising a member'having ope-n ends, reticuli'ite members covering said en s, said members being of dilierent degrees of fineness, and a pair of electrodes carried by -said casing and having co-operating end portions disposed within said casing in predetermined spaced relation.

10. Discharge apparatus comprising air electrode of copper-nickel allov having a the shields from operating to formation of a crater by the discharge.

11. in a glow discharge device, a negative" electrode comprising Advance Wire.

12. The combination with a discharge apparatus, of a pair of electrodes disposed in the discharge, said electrodes comprising an alloy of nickel and copper, having a melting point low relative to its oxidation point.

13. The combination with a discharge apparatus. comprising. electrodes at the terminals of the discharge, of a pair of electrodes disposed in the discharge, said electrodes comprising an alloy of nickel and copper, in which the copper exceeds the nickel.

14. In combination, apair of spaced electrodes open to the air, means forestablishing a glow-discharge therebetween, said dissufficiently low melting point to prevent the i charge including a Faraday dark space and other portions, and means responsive to variations of an electrical characteristic of said dark space only for delivering corresponding electric currents. i 1- 1 5. In a discharge apparatus, a pair of terminals exposed to atmosphere pressure, means for maintaining a discharge between said terminals, anadditional electrode situated within said discharge and an output circuit associated with said additional electrode, said additional electrode being con posed of an alloy of nickel and copper.

16. In a discharge apparatus, aipair of terminals exposed to atmosphere pressure, means for maintaining a discharge between said terminals, a pair of additional electrodes situated-within said discharge and an output circuit associated with said additional electrodes.

In testimony whereof, I have hereunto subscribed my name this 10th day of November 1922.

PHILLIPS THOMAS. 

